The past few months I've had more students inquire about how major and minor key signatures work, which is one of my many favorite music theory concepts to help them with. I start working with them explaining how the major keys work based on sharps (looking at the last sharp and going up a half a step) and flats (looking at the second to last flat) to determine what key a song is in. Show them the Circle of 4ths and 5ths with the visual flash cards and have music alphabet flash cards with all the Key Signatures . We take it deeper with the visuals, where I show them how C Major has no sharps or flats and how Cb and C# have 7, How D Major has two sharps and Db Major has 5 Flats, G Major has one sharp and Gb and G# Major have 6. It's all based on 7's. I have flash cards from susanparadis.com, that are helpful explaining key signatures, yet it appears to not be on her website. She does have a fun game called Nine Keys and here is the link:
Here is a link of flash cards from pianoanne.ca, will help you and your students.
When it comes to transposing I focus on a simple song that a student can play quickly, like Mary Had a Little Lamb. I have them play in the key of C Major (which only uses a C and G Major Chords) and then we use the key signature cards and have them play the melody in other keys. I determine the 1 and 5 chord of the keys and give them the start of the melody. My favorite part is when it starts clicking. I will even find chord sheet songs with 2 or 3 chords and have them change keys to the song. They really enjoy it.
What I'm sharing is just the tip of key signatures and transposing. How do you teach it? Would like to know. Hopefully I can share more about these and other techniques to help musicians be successful with transposing and key signatures. Thanks for your support. Blessings.